They are complicated but they do work. Constantly lubed and away from dirt and water. They are a pain to get at and more of a pain to put back together, especially when the shop manual tells you to adjust the ball housing with shims so that it is "not too tight or not too loose!" The weak point is in the small bolts they use to hold the trunion in place. When you figure that these 4 bolts are all that is taking the torque from the motor to the wheels.
I don't know of any replacement other than going to another trans and diff.
